1. Field of the Invention
The present invention relates to a laser pointing apparatus and in particular, to a laser pointing apparatus having a small size and small weight and capable of controlling a high-accuracy positioning. Moreover, the present invention relates to an on-fulcrum movement drive apparatus for use in the laser pointing apparatus and an antenna and a mirror which are located in an outer space.
2. Description of the Related Art
[A] Firstly, explanation will be given on a conventional laser pointing apparatus.
A laser beam machining apparatus and a laser display apparatus, a laser scan apparatus, and the like, in general, employ a laser pointing apparatus for controlling a laser beam emission angle or a laser beam incident angle.
In most of the conventional laser pointing apparatuses, two mirrors are used in combination for scanning a two-dimensional plane with a laser beam. However, there is a strong desire for reduction in the apparatus size and production cost as well as for simplification of a procedure for optical axis matching and positioning.
In order to satisfy these requirements, for example, Japanese Patent Publication (Unexamined) A-7-185866 discloses an apparatus including a single mirror, a rotary support member which can rotate around a normal axis of the mirror, and a mirror positioning mechanism supported by the support member. In this apparatus, a two-dimensional plane can be scanned by a laser beam using the single mirror.
Hereinafter, explanation will be given on some examples of conventional laser pointing apparatus with reference to the attached drawings.
FIG. 21 is a side cross sectional view of a conventional laser pointing apparatus including: a mirror 101; an electromagnetic exciter 105 for moving the mirror 101; a rotary support member 106 for supporting the mirror 101 and the electromagnetic exciter 105; and a motor rotating the rotary support body 106.
The mirror 101 can be deflected around the Z axis by rotation of the rotary support member 106 driven by the motor 109 and also deflected around the oscillation center 103. This enables a laser beam to scan any position on a two-dimensional plane with the single mirror.
[B] Next, explanation will be given on a conventional on-fulcrum movement drive apparatus.
An antenna mounted on an artificial satellite or other space object is positioned by an on-fulcrum movement drive apparatus so as to assure a preferable communication with an earth station. The on-fulcrum movement drive apparatus moves the antenna around the X axis and Y axis which vertically intersects the X axis. Conventionally, this positioning around two axes has been effectuated by using a support mechanism having two bearings arranged vertical to each other. Moreover, this type of on-fulcrum movement drive apparatus is employed not only for an antenna but also for positioning a mirror and driving a positioning table.
In general, for the apparatuses to be mounted on an artificial satellite, there is a strong requirement for reduction in size and weight. The on-fulcrum movement drive apparatus has also been improved in various ways to satisfy the aforementioned requirement. For example, Japanese Patent Publication (Unexamined) A-53-34499 discloses an on-fulcrum movement drive apparatus in which an object to be driven is supported at a single point of a spherical bearing.
FIG. 22 is a cross sectional view of such a conventional on-fulcrum movement drive apparatus. The on-fulcrum movement drive apparatus shown in FIG. 22 includes: an antenna 301 as an object to be positioned; a spherical bearing 302 for movably supporting the antenna 301; a piston 303 for driving the antenna 301; a linear motor 304 for driving the piston 303; a sensor 305 for detecting displacement of the linear motor 304; and a spring 306 for pushing the antenna 301 toward the piston 303.
According to a detection result of displacement detected by the sensor 305, the linear motor 304 drives the piston 303 and the antenna 301 is moved around the spherical bearing 302 as a fulcrum.
Although not depicted, another set of a piston, a linear motor, and a sensor is arranged in a direction vertically intersecting the drive direction of the piston 303. Thus it is possible to obtain a movement around two axes.
However, the conventional laser pointing apparatus and the conventional on-fulcrum movement drive apparatus have following problems.
[A] Firstly, explanation will be given on the problems involved in the conventional laser pointing apparatus.
The first problem is that the conventional laser pointing apparatus is too large in size because it employs an electromagnetic exciter and a motor having a large volume.
The second problem is that the apparatus is too heavy because the rotary support member requires a comparatively high support strength and becomes heavy. Accordingly, the motor for driving the rotary support member also becomes heavy.
The third problem is that a large power consumption is required. This is because rotation of the mirror around the normal requires rotation of not only the mirror but also the large-mass positioning mechanism constituted by the electromagnetic exciter and the rotary support member.
The fourth problem is that it is difficult to control a pointing position with a high accuracy. This is because the rotation is driven by a motor and a belt. That is, non-linear elements such as the motor torque ripple and the belt expansion/shrinking are involved in the control system.
[B] Next, explanation will be given on the problems involved in the conventional on-fulcrum movement drive apparatus.
The first problem is that it is difficult to control positioning with a high accuracy. That is, the spherical bearing 302 cannot eliminate fluctuation and friction. During a drive, non-linear external components are involved in the control system, lowering the positioning accuracy.
The second problem is that the conventional on-fulcrum movement drive apparatus cannot be used in an outer space. In order to maintain a predetermined sliding characteristic on the spherical bearing 302, a certain amount of lubricant should be present. However, this is difficult in an outer space where a lubricant easily volatilizes.
It is therefore an object of the present invention to provide a laser pointing apparatus small in size and weight and capable of a highly accurate positioning with a reduced power consumption.
Another object of the present invention is to provide an on-fulcrum movement drive apparatus which can perform positioning with a highly accurate angle and which can also be used in an outer space.
The laser pointing apparatus according to the present invention is for pointing a laser beam on a predetermined position and comprises: a mirror extending on a X-Y plane and having a mirror surface for reflecting the laser beam; a mirror holder arranged so as to be displaceable and having a mirror holder main body for holding the mirror and at least three arms extending outwardly from the mirror holder main body; an elastic support mechanism for supporting the mirror holder main body according to the displacement of the mirror holder around a point on a Z axis passing through the center of the mirror and vertically intersecting the X-Y plane; a base for supporting the elastic support mechanism;
coil type electromagnets (hereinafter, referred to as coil magnets) arranged on the respective arms so as to generate a line of magnetic force in the Z axis direction; and permanent magnets provided on the base facing the corresponding coil magnets so as to generate a line of magnetic force in the Z axis direction,
wherein a magnetic force generated by interaction between the permanent magnets and the coil magnets supports the mirror holder in such a manner that the mirror holder can be translated in the Z axis direction and also rotated around the mirror center.
According to another aspect of the present invention, the laser pointing apparatus comprises: a mirror extending on a X-Y plane and having a mirror surface for reflecting the laser beam; a mirror holder arranged so as to be displaceable and having a mirror holder main body for holding the mirror and at least three arms extending outwardly from the mirror holder main body; an elastic support mechanism for supporting the mirror holder main body according to the displacement of the mirror holder around a point on a Z axis passing through the center of the mirror and vertically intersecting the X-Y plane; a base for supporting the elastic support mechanism;
permanent magnets arranged on the respective arms so as to generate a line of magnetic force in the Z axis direction; and coil magnets provided on the base facing the corresponding coil magnets, so as to generate a line of magnetic force in the Z axis direction,
wherein a magnetic force generated by interaction between the permanent magnets and the coil magnets supports the mirror holder in such a manner that the mirror holder can be translated in the Z axis direction and also rotated around the mirror center.
That is, according to the present invention, the drive source includes only coil magnets and permanent magnets. Thus, the apparatus is small in size and weight. Moreover, the object to be driven includes only the mirror, mirror holder, arms, and the coil magnets which have small weights, enabling to significantly reduce the power consumption required for the drive compared to a conventional apparatus. Furthermore, the coil magnets and permanents serving as the drive source do not cause any friction in the drive mechanism as in a conventional apparatus. That is, no non-linear element is involved in the drive source, which enables to perform positioning with a high accuracy.
In the aforementioned apparatuses, the translation in the Z-axis direction may not be used.
It is preferable that the elastic support mechanism support the mirror holder in such a manner that the mirror holder can rotate around the X and Y axes on the X-Y plane. In this case, it is preferable that the elastic support mechanism be constituted by a pivot provided on the Z axis for supporting a rear surface of the mirror holder and a plate spring having a tip end attached to the tip end of the pivot.
In the laser pointing apparatus having the aforementioned configuration, a current is applied to the coil magnets, so that a force is generated between the coil magnets and the permanent magnets, generating a moment of rotation around the X and Y axes vertically intersecting each other on the mirror surface. This moment moves the mirror simultaneously in two directions so that any position on the two-dimensional plane can be scanned by a laser beam.
Moreover, it is preferable that the laser pointing apparatus further comprise: distance displacement sensors for detecting a Z-axis direction displacement from a stationary position of a reference point on each of the arms; and a control block for receiving signals from the distance displacement sensors to calculate an angle (hereinafter, referred to as an angular displacement) of rotation of the mirror from the stationary position, and adjusting coil currents to be applied to the coil magnets according to the relationships between the permanent magnets and the coil magnets, thus controlling the angular displacement.
In this case the control block, for example, includes: angle calculation means for calculating an angular displacement from the position displacement values detected by the distance displacement sensors; an angle specifier for specifying a target angular displacement; angle control means for calculating coil current adjustment values for the respective coil magnets so that the angular displacement calculated is matched with the target angular displacement, and for generating coil current instruction signals instructing to apply coil currents of the calculated values to the respective coil magnets; and a coil magnet driver circuit for applying currents to the respective coil magnets according to the coil current instruction signals.
The reference point is a measurement point where a mirror angular displacement can be sufficiently detected from the Z-axis direction position displacement.
Furthermore, the elastic support mechanism can move the mirror holder in the Z-axis direction; and the control block may further include: translation amount calculation means for calculating an average value of the respective arm displacement in the Z-axis direction so as to obtain an average translation distance (hereinafter, referred to as an actual translation amount) of the mirror in the Z-axis direction; a translation amount specifier for specifying a target translation amount (hereinafter, referred to as a target translation amount); translation amount control means for calculating a second adjustment value of the coil current which causes the actual translation amount to be matched with the target translation amount, and for generating a coil current adjustment signal; and a translation amount regulator for adding the coil current instruction signal to the coil current adjustment signal to obtain a new coil current instruction signal to be transmitted to the coil magnet driver circuit.
This enables to control displacement of the mirror in the Z axis direction as well. Thus, the laser pointing apparatus can prevent unintentional movement of the laser beam pointing.
According to yet another aspect of the present invention, there is provided an on-fulcrum movement drive apparatus for moving an object to be driven around two imaginary axes vertically intersecting each other, the apparatus comprising: a frame for supporting the object to be driven; an elastic support mechanism provided between the frame and the object to be driven, for supporting the object to be driven at one point on the rear surface of the object, so that the object is movably mounted on the frame; and an actuator provided on the frame for moving the object to be driven, by applying a force to a position on the object which is apart from the support position supported by said elastic support mechanism.
In the on-fulcrum movement drive apparatus, the object to be driven is supported on one point of its rear surface by an elastic support mechanism made from an elastic material in such a manner that the object can be moved around the aforementioned one point. Thus application of force by actuators to the object can move the object around two axes vertically intersecting each other.
Moreover, because the object to be driven is fixed to the elastic support mechanism, there is no fluctuation or friction such as in the case of spherical bearing. No no-linear external component is involved in the control system during a drive period. This enables to control the angle of the object with a high accuracy.
Furthermore, in contrast to the spherical bearing which requires a lubricant, the apparatus of the present invention has no problem of lubricant evaporation and can be used in a vacuum such as in an open space.